LONDON (Reuters) - Older women may be more prone to suffer
from osteoporosis because they do not have enough receptors, or chemical
doorways, for the female hormone estrogen, scientists said on Wednesday.
Osteoporosis, or brittle bone disease, affects about one
in three women and is more common after the menopause when the body makes
less estrogen.
Normally when a bone is subjected to repeated mechanical
stress, new bone cells compensate for the load. But Professor Lance Lanyon
and researchers at The Royal Veterinary College in London have discovered
that in transgenic mice lacking an estrogen receptor called ER-alpha, this
does not happen.
"It is the first time ER-alpha has been implicated in
bones' normal adaptive response to mechanical loading," Lanyon said in an
interview.
"The estrogen receptor is involved in the response to
mechanical loading which is responsible for establishing and maintaining
bone mass. We think that is the critical link why when you take away the
reproductive hormone, you lose bone," he added.
Hormone replacement therapy (HRT), which replenishes the
hormone loss after menopause, is prescribed to prevent osteoporosis but it
can increase the risk of heart disease, strokes and some cancers.
"The rationale for why hormone replacement therapy
prevents osteoporosis is that if it has estrogen in it, it maintains
estrogen receptor numbers," said Lanyon.
But the disadvantage is that high estrogen receptors in
breast or uterine tissue could increase the likelihood of developing cancer
in those areas.
Lanyon believes his findings, which are reported in the
science journal Nature, could lead to the development of new drugs that
could enhance the performance of the receptor for bone density without
increasing cancer risk.
"The future trick would be to get an organ or
tissue-specific enhancement of estrogen receptor activity just for the bones
and not for the other tissues," he added.
Lanyon said the research points to a specific therapeutic
strategy to prevent osteoporosis and answers the long-standing puzzle about
why removing a reproductive hormone results in bone loss.
SOURCE: Nature, 2003.
